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A/B Testing Encryption Strength (Per-User) Calculator

Compare the estimated brute-force resistance and per-user compromise likelihood of two encryption strength settings.

Your Details

Overview

Use this calculator to compare two encryption strength settings on a per-user basis. Enter each version's effective security strength, a hypothetical attack guessing rate, the time available to attack each user, and the number of users protected by independent keys.

How it works

A strength of n bits represents approximately 2 raised to the power of n possible keys. The calculator estimates average brute-force work as half of that keyspace, then divides by the entered guess rate to estimate time. For the selected attack period, it estimates a per-user compromise likelihood from the fraction of the keyspace searched. It then applies that likelihood to the number of independently protected users to show population-level estimates. These figures describe a simplified brute-force model only.

How to use this calculator

  1. 1Enter the effective security strength in bits for version A.
  2. 2Enter the effective security strength in bits for version B.
  3. 3Set a hypothetical number of valid brute-force guesses per second.
  4. 4Enter the attack duration available for each user.
  5. 5Add the number of users with independently generated keys.
  6. 6Compare the per-user likelihoods, expected crack times, and population estimates.

Example Calculation

Version A security strength

128

Version B security strength

256

Attack guesses per second

1000000000000

Attack duration per user

1

Number of independently protected users

1000000

Version B strength difference

+128 bits

With a hypothetical rate of 1 trillion guesses per second for one year per user, version B has 128 more bits of stated brute-force strength. Both per-user likelihoods are extremely small in this simplified model, while the estimated brute-force time for 256-bit strength is vastly longer than for 128-bit strength.

Frequently asked questions

What does “per-user” mean in this calculator?

It assumes each user has a separate, independently generated encryption key and that the entered attack effort can be applied to one user's key at a time.

Why does a small increase in bits make such a large difference?

Each additional bit doubles the keyspace. A 256-bit keyspace is 2 raised to the power of 128 times larger than a 128-bit keyspace.

Does this calculate the real chance that encryption will be broken?

No. It estimates brute-force key guessing under the assumptions entered. It does not model weak passwords, flawed implementations, exposed keys, side channels, or new attacks.

Why is expected crack time based on half the keyspace?

If the correct key is uniformly random and every possible key is searched systematically, it is found halfway through the keyspace on average.

Can I use this for password-derived encryption keys?

Only with care. Password-derived keys are often limited by password entropy and the key-derivation process, not merely by the encryption algorithm's nominal key size.

Why might the population estimate differ from the per-user estimate?

Even a very small per-user likelihood can become more relevant across many independently protected users, because there are more opportunities for at least one compromise.

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Assumptions and warnings

Assumptions

  • Each user has a separate, uniformly random encryption key with the stated effective security strength.
  • The attacker performs valid brute-force guesses at a constant rate for the full period entered.
  • Attack effort is evaluated per user rather than shared across a single common key or password.
  • The per-user compromise likelihood is approximated from the proportion of the keyspace searched.
  • Expected crack time assumes a successful exhaustive search finds a random key halfway through the keyspace.
  • Results are estimates and do not account for implementation flaws, side channels, stolen keys, or cryptanalytic breakthroughs.

Warnings

  • This calculator models brute-force guessing only; real-world encryption security can be limited by key management, passwords, software flaws, and operational controls.
  • Use the results as a comparison aid, not as the sole basis for security design or risk decisions.